pthreads_create () returns non-zero value?

Question

I have created a function to set attributes of a pthread before calling pthread_create(). However, pthread_create() is failing as it returns non-zero value. I am not sure what is wrong with the attributes set by my function. I am compiling my program with g++ on Ubuntu 16.04 LTS.

To compile and execute i am using:

g++ example.cpp -lpthread
./a.out

-

typedef void *(*DART_TASK_T)(void *);
typedef void (*DART_CALLBACK_T)(int);

static struct taskcontrolblock_s sysTask[MAX_DARTOS_THREADS];
static unsigned max_task_id_registered = 0;

static std :: bitset<sizeInBytes(MAX_DARTOS_THREADS)> taskIDs;

struct taskcontrolblock_s {
    const char *name;

    DART_TASK_T routine;
    DART_CALLBACK_T cleanup_callback;

    void *arg;
    unsigned arg_len;

    union {
        uint8_t flags;
        struct {
        //uint8_t created:1;
        //uint8_t running:1;
        //uint8_t blocked:1;
        //uint8_t suspended:1;
        //uint8_t killed:1;
        //uint8_t completed:1;
        //uint8_t;
        }; 
    };

    int priority; 

    pthread_t thread;
}__attribute__((packed));


static int dispatch_task(int tid)
{
    if (!taskIDs[tid]) // 
        return -1;

    pthread_attr_t attr;
    struct sched_param param;
    param.sched_priority = sysTask[tid].priority;
    int policy = SCHED_RR;

    if (pthread_attr_init(&attr))
        return -1;
    if (pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED))
        return -1;
    if (pthread_attr_setschedpolicy(&attr, policy))
        return -1;
    if (pthread_attr_setschedparam(&attr, &param))
        return -1;
    if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM))
        return -1;

    if (pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED))
        return -1;

    if (pthread_create(&sysTask[tid].thread, &attr, sysTask[tid].routine, sysTask[tid].arg))
    return -1;

    pthread_attr_destroy(&attr);
    return 0;
}

Edit:

Calling perror() prints the character array Operation not permitted to the stderr.

Running the program with root privilege solved the problem.

You're leaving some members of `struct sched_param param` uninitialized. — Jonathon Reinhart, Dec 20 '16 at 11:36
use perror() to display the cause of the failure that would help us to understand whats wrong. — A.N, Dec 20 '16 at 11:38
Note that only root user would be allowed to set the scheduler to SCHED_RR — nos, Dec 20 '16 at 11:39
@nos: executing `binary` with root privilege solved the problem. How can i execute it without root privilege? — abhiarora, Dec 20 '16 at 11:46
@abhiarora you should capture return value from pthread_xx functions and set errno = retval before calling perror.. check man pthread_create for sample on how to do it.. — A.N, Dec 20 '16 at 11:47
Using SCHED_RR can potentially freeze your computer. Do you really need it? — koalo, Dec 20 '16 at 11:50
@LightnessRacesinOrbit Does `std::thread` support OS-specific attributes equivalent to `PTHREAD_SCOPE_SYSTEM`, `PTHREAD_CREATE_DETACHED`, `PTHREAD_EXPLICIT_SCHED`, or `SCHED_RR`? — Andrew Henle, Dec 20 '16 at 12:09
@AndrewHenle: Detaching a thread, yes certainly. Otherwise you can set whatever OS-specific attributes you like, using the native handle getter (http://stackoverflow.com/a/18884807/560648). Whether that's sufficient I don't know - might make a good SO question! — Lightness Races in Orbit, Dec 20 '16 at 12:30

score 2 · Accepted Answer · edited May 23 '17 at 11:45

2

The first part of the answer is that to use SCHED_RR you must have CAP_SYS_NICE for your user. As you have noted, running as root makes it work. But you can run as any user so long as you have the CAP_SYS_NICE "capability." One way to get that is using setcap which is explained here: https://stackoverflow.com/a/37528755/4323

You will need the ability to run sudo setcap.

edited May 23 '17 at 11:45

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answered Dec 20 '16 at 12:04

John Zwinck

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pthreads_create () returns non-zero value?

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